I am an Assistant Member at Fox Chase Cancer Center (Philadelphia, PA) and I am submitting a K01 application to study the new biology of estrogen and fulvestrant action in aromatase inhibitor resistant breast cancer cells. Project Summary: Aromatase inhibitors (Als) are currently accepted as the standard care for the treatment of estrogen receptor (ER)-positive breast cancer. These agents prevent estrogen synthesis in postmenopausal women. One of the consequences of long-term estrogen deprivation (i.e., aromatase inhibition), however, is the development of acquired drug resistance. To further study the development of acquired resistance to Als, I have developed a panel of long-term estrogen deprived (LTED) breast cancer cell lines that were adapted to grow under estrogen-depleted conditions. The phenotype of these LTED cells is that they grow robustly in the absence of estrogen (i.e., resistant to estrogen deprivation), however, in the presence of physiologic concentrations of 17 (-estradiol (E2), these Al-resistant cells undergo cell death. The mechanism by which estrogen switches from being a growth stimulus (cancer-causing agent) to a killing (apoptotic) agent is not known. The goal of my research project is to investigate the new biology of E2 action in long-term estrogen deprived breast cancer cells. The hypothesis is that long-term estrogen deprivation alters the milieu of a select subset of breast cancer cells which sensitizes them to estrogen-induced death. The following research techniques will be used;Western blot analysis to measure protein expression, Real-Time polymerase chain reaction (PCR) to measure changes in mRNA levels, confocal microscopy to study protein translocalization, small interfering RNA (siRNA) and transfection analyses to suppress gene expression, cell invasion and migration assay to measure invasiveness and metastatic potential of Al-resistant cells, and chromatin immunoprecipitation (ChIP) assay to measure ER interaction with coregulatory proteins at estrogen-responsive promoters. Relevance of Research Project: The American Cancer Society has estimated that in 2006, approximately 212,920 women in the United States will be diagnosed with breast cancer and 40,970 will die. Breast cancer thus represents a major health problem;hence, a strategy to understand and subvert the acquisition of resistance to current treatment modalities would be a valuable therapeutic advantage.